Carbon-Negative Cement Manufacturing from Seawater-Derived Magnesium Feedstocks

This study describes and demonstrates a carbon-negative process for manufacturing cement from widely abundant seawater-derived magnesium (Mg) feedstocks. In contrast to conventional Portland cement, which starts with carbon-containing limestone as the source material, the proposed process uses membrane-free electrolyzers to facilitate the conversion of carbon-free magnesium ions (Mg2+) in seawater into magnesium hydroxide (Mg(OH)2) precursors for the production of Mg-based cement. After a low-temperature carbonation curing step converts Mg(OH)2 into magnesium carbonates through reaction with carbon dioxide (CO2), the resulting Mg-based binders can exhibit compressive strength comparable to that achieved by Portland cement after curing for only two days. Although the proposed “cement-from-seawater” process requires similar energy use per ton of cement as existing processes, its potential to achieve a carbon-negative footprint makes it highly attractive to decarbonize one of the most carbon intensive industries.

Carbon-Negative Cement Manufacturing from Seawater-Derived Magnesium Feedstocks

This study describes and demonstrates a carbon-negative process for manufacturing cement from widely abundant seawater-derived magnesium (Mg) feedstocks. In contrast to conventional Portland cement, which starts with carbon-containing limestone as the source material, the proposed process uses membrane-free electrolyzers to facilitate the conversion of carbon-free magnesium ions (Mg2+) in seawater into magnesium hydroxide (Mg(OH)2) precursors for the production of Mg-based cement. After a low-temperature carbonation curing step converts Mg(OH)2 into magnesium carbonates through reaction with carbon dioxide (CO2), the resulting Mg-based binders can exhibit compressive strength comparable to that achieved by Portland cement after curing for only two days. Although the proposed “cement-from-seawater” process requires similar energy use per ton of cement as existing processes, its potential to achieve a carbon-negative footprint makes it highly attractive to decarbonize one of the most carbon intensive industries.

Magnesium Signaling in Plants

Free magnesium (Mg2+) is a signal of the adenylate (ATP+ADP+AMP) status in the cells. It results from the equilibrium of adenylate kinase (AK), which uses Mg-chelated and Mg-free adenylates as substrates in both directions of its reaction. The AK-mediated primary control of intracellular [Mg2+] is finely interwoven with the operation of membrane-bound adenylate- and Mg2+-translocators, which in a given compartment control the supply of free adenylates and Mg2+ for the AK-mediated equilibration. As a result, [Mg2+] itself varies both between and within the compartments, depending on their energetic status and environmental clues. Other key nucleotide-utilizing/producing enzymes (e.g., nucleoside diphosphate kinase) may also be involved in fine-tuning of the intracellular [Mg2+]. Changes in [Mg2+] regulate activities of myriads of Mg-utilizing/requiring enzymes, affecting metabolism under both normal and stress conditions, and impacting photosynthetic performance, respiration, phloem loading and other processes. In compartments controlled by AK equilibrium (cytosol, chloroplasts, mitochondria, nucleus), the intracellular [Mg2+] can be calculated from total adenylate contents, based on the dependence of the apparent equilibrium constant of AK on [Mg2+]. Magnesium signaling, reflecting cellular adenylate status, is likely widespread in all eukaryotic and prokaryotic organisms, due simply to the omnipresent nature of AK and to its involvement in adenylate equilibration.

Rare-earth- and aluminum-free, high strength dilute magnesium alloy for Biomedical Applications

Lightweight, recyclable, and plentiful Mg alloys are receiving increased attention due to an exceptional combination of strength and ductility not possible from pure Mg. Yet, due to their alloying elements, such as rare-earths or aluminum, they are either not economical or biocompatible. Here we present a new rare-earth and aluminum-free magnesium-based alloy, with trace amounts of Zn, Ca, and Mn (≈ 2% by wt.). We show that the dilute alloy exhibits outstanding high strength and high ductility compared to other dilute Mg alloys. By direct comparison with annealed material of the same chemistry and using transmission electron microscopy (TEM), high-resolution TEM (HR-TEM) and atom probe tomography analyses, we show that the high strength can be attributed to a number of very fine, Zn/Ca-containing nanoscale precipitates, along with ultra-fine grains. These findings show that forming a hierarchy of nanometer precipitates from just miniscule amounts of solute can invoke simultaneous high strength and ductility, producing an affordable, biocompatible Mg alloy.

Study of Polarization Characteristics of Corrosion Films on Magnesium in Sulfate-Containing Electrolytes

In this article, the results of studying the polarization characteristics of magnesium covered with corrosion film in aqueous solutions of MgSO4 and Na2SO4 are presented. The absence of a corrosion-free magnesium surface was shown; in this connection, it was proposed to interpret the larger values of Tafel’s coefficients obtained in the experiment from the point of view of limiting the electrochemical process by charge transfer in the film phase. Charge transfer in corrosion films obeys the regularities of particle movement in high electric fields, and it is not only cationic. According to the impedance measurements, the resistance of the oxide and hydroxide layer of the magnesium-based corrosion film in the studied solutions was calculated. The largest contribution to the restriction of charge transfer in the initial stages of corrosion is made by a dense primary film defining the polarization resistance. Correlation of transfer parameters in high electric fields with thickness and resistance of corrosion film was demonstrated.